1. Field of the Invention
The present invention relates to a serial scanning ink jet printing apparatus that performs a printing operation by scanning a print head in a direction crossing a direction in which print media are conveyed. In particular, the present invention relates to an ink jet printing apparatus in which in order to maintain the proper ejecting performance of a print head, ink is ejected into an ink receiving portion provided at a position opposite a scan area for the print head, to recover the performance of the print head. The present invention also provides a method for recovering the ink jet printing apparatus.
2. Description of the Related Art
An ink jet printing apparatus outputs an image by ejecting a liquid such as ink from an ink jet print head (hereinafter simply referred to as a print head) onto a print medium in accordance with input image data. Thus, a maintenance technique for maintaining the proper ink ejection state of the print head is a very important factor for forming high quality images. Now, a simple explanation will be given of the major reason for the need for the maintenance of the print head (this operation is hereinafter referred to as a performance recovering operation).
(a) During printing of input image data, ink may be evaporated from nozzles from which ink is not ejected among a plurality of nozzles arranged in the print head. This may make the ink in those nozzles more viscous. In this case, ink cannot be stably ejected by normal ink ejection energy, resulting in improper ejection.(b) During printing, ink droplets ejected from the nozzles may involve fine ink droplets (which are also called mists) different from main ink droplets that land on the print medium. The fine ink droplets may adhere to the periphery of ink ejection openings in the print head. This may prevent the direct advancement of ejected ink droplets.(c) When bubbles are present in an ink reservoir in the print head, gas having passed through members constituting the ejection openings or print head may be taken in by the bubbles, which may thus grow. The bubbles may also be expanded by a temperature increase during printing. In this case, an ink supply from an ink tank is hindered by the expanded bubbles, resulting in improper printing.
The following have been known as maintenance techniques for solving the problems in (a) to (c).
(A) In a period or an environment in which ink is not ejected, an operation of ejecting a predetermined amount of ink is preformed which is different from an ink ejecting operation for forming an image on a print medium. This allows ink having become more viscous in the nozzle to be discharged. This operation is hereinafter referred to as preliminary ejection.(B) The number of ink droplet ejections from the ejection openings is counted. If the count exceeds a predetermined value, a rubber blade or the like is used to sweep a surface (hereinafter referred to as an ejection opening formed surface) of the ink jet print head on which the ejection openings are formed. This removes ink adhering to the ejection opening formed surface. This operation is hereinafter referred to as wiping.(C) A recovery operation is performed by using a pump to suck ink out of the nozzle ejection openings to discharge ink from the nozzles. This operation is hereinafter referred to as suction recovery. For an ink jet printing apparatus in which the print head and the ink tank can be separated from each other and in which the ink tank is replaceable, the suction recovering operation is also performed after replacement of the ink tank.
In one of these recovery operations, that is, preliminary ejection, particularly preliminary ejection during a printing operation, ink is ejected into a cap that can seal the ejection opening formed surface or a preliminary ejection receiving portion provided opposite a scan path for the print head. In this case, the cap is held at an appropriate distance from the print head (at a lowered position).
On the other hand, the cap plays such a role as to keep the ejection opening formed surface of the ink jet print head sealed in order to prevent the ejection opening formed surface from being dried. The cap is also used for a pressurizing recovery operation of applying air pressure to the inside of the nozzle to discharge ink or for the above suction recovery operation. The suction recovery operation maintains the cap at a position (elevated position) where it seals the ejection opening formed surface to receive ink ejected from the print head.
Thus, to execute preliminary ejection on the cap, it is necessary to lower the cap by an appropriate distance from the ejection opening formed surface of the print head. Ink collected in the cap as a result of preliminary ejection also needs to be discharged during a printing operation. Moreover, ink scattering during preliminary ejection may result in, for example, contamination of the cap and its surroundings. With these inconveniences taken into account, a configuration is more advantageous which preliminarily ejects ink into an ink receiving portion in which only an opening with a given space is formed. This configuration is more advantageous because of its simplified mechanisms and control compared to the configuration that preliminarily ejects ink into the cap.
If an ink receiving portion is used to receive preliminarily ejected ink, it is generally configured so that ejected ink collected in the ink receiving portion is held by a waste ink absorbing portion provided opposite (inside) the ink receiving portion. A channel through which the ink ejected into the ink receiving portion is guided to the waste ink absorbing portion is shaped so as not to disturb the natural fall of the ink based on its gravity.
However, recent printers, the sizes of which tend to be reduced, may limit the space in which the ink receiving portion is installed. Specifically, a sheet feeding mechanism, a head cleaning mechanism, and the like are arranged within the range of the path along which a carriage executes scanning. Accordingly, the need to avoid the interference between these mechanisms and the ink receiving portion makes it difficult to design the channel through which ink is guided from the ink receiving portion to the waste ink absorbing portion as well as the shape of the ink receiving portion. For example, the ink receiving portion may have to be partly constricted; the ideal design may be impossible.
Thus, in an ink jet printing apparatus using ink less soluble than the conventional ink, the less soluble ink may accumulate in the ink receiving portion or a channel. As a result, the deposit may block the channel. In this case, the deposit may disadvantageously overflow or contact the ejection opening formed surface. The term called deposit here means what mainly color material and ink solvent or the like solidify.
Japanese Patent Laid-Open No. 7-323574 discloses means for solving these problems, that is, a mechanism that scrapes off adhering deposit.
Japanese Patent Laid-Open No. 9-30004 discloses an operation of removing deposit onto the ink receiving portion which operation is different from the ejection operation serving as the recovering operation for the print head.
Japanese Patent Laid-Open No. 2003-72106 discloses a technique of dividing a spit position into plural positions and preliminarily ejecting ink so that the ink is distributed to the respective spit positions to reduce the height of the ink heap.
However, the technique disclosed in Japanese Patent Laid-Open No. 7-323574 disadvantageously increases the width of the printing apparatus and the number of components to complicate the mechanism and control. This prevents size and cost reduction.
Further, the technique disclosed in Japanese Patent Laid-Open No. 9-30004 carries out ink ejection to remove deposit independently of the preliminary ejection for the recovering operation for the print head. This disadvantageously increases ink consumption and thus running costs.
Further, Japanese Patent Laid-Open No. 2003-72106 discloses a technique for performing a spit operation at a certain spit position and performing the next spit operation at a different spit position. This technique is effective in varying the ink spitting position to disperse the deposit in the ink receiving portion without concentrating it in one area to reduce its height. However, this technique does not remove the deposit itself. In other words, ink is spat at different positions to reduce the height of the ink deposit. Accordingly, this is not a measure for suppressing the deposit generation itself. Therefore, if preliminary ejection is frequently carried out or viscous ink is used, the amount of ink deposit itself apparently increases.